1. Field of the Invention
The present disclosure relates to electrical distribution equipment, and more particularly, to testing components in an electrical switchgear system.
2. Description of the Related Art
A switchgear system receives electrical power from an electric utility company and distributes the electrical power at a customer site. Such a system typically includes devices such as current transformers (CT), potential transformer (PT), also known as voltage transformers, human machine interface devices to display metering data, e.g., kilowatts-hours, circuit breakers, and protection relays in addition to circuit breakers.
The switchgear system also includes a controller, referred to as a node, associated with each circuit breaker. The node monitors signals such as current from a CT and voltage from a PT, and based on the condition of the signals, controls the circuit breaker with which the node is associated. For example, if the node determines that the current exceeds a predetermined value, the node can control the circuit breaker to trip, i.e., open.
Industrial power distribution systems commonly divide incoming power into a number of branch circuits, where the branch circuits supply power to various equipment (i.e., loads) in an industrial facility. Circuit breakers are provided in each branch circuit to facilitate protection of equipment within the branch circuit. Accordingly, the switchgear system would include a plurality of nodes.
Switchgear systems are typically tested by applying or manipulating currents and voltages at or near normal operating levels. As such, the tests employ high current sources and high voltage sources, and test signals are injected at only one point in the system at a time. High voltage test equipment is typically expensive as compared to low voltage equipment. Also, high voltage testing presents more safety concerns to test personnel than ordinarily exist for low voltage testing. Furthermore, many tests require a part of the system, or perhaps the full system, to be taken off-line during the tests.
Some test solutions only establish a communication link with a device under test. For example, consider a test kit that interfaces with a trip unit under test via a three-wire digital communication link through a test jack on the trip unit. Such a test kit only allows for simulation of time-overcurrent conditions on a single breaker, and so it does not provide for testing of coordinated protection functions such as modified differential ground fault and bus differential. Furthermore, this type of test kit does not inject actual voltages or currents, but rather digital signals representing current or voltage levels. Also, some components, analog to digital converters for example, are not tested when communication link test methods are used. Consequently, this test kit alone does not fully exercise or test the trip unit.